1. Field of the Invention
The present invention relates to Air Traffic Control (ATC) automated aircraft conflict prediction, and, more particularly, to strategic, trajectory-based methods that utilize surveillance data (e.g., radar position reports) to monitor trajectory accuracy.
More particularly, the present invention relates to the reevaluation of variable conformance bounds and predicted aircraft positions over the first several minutes of lookahead time based on the observed aircraft track and navigational equipage. Further, it relates to a system and method for providing timely updates based on observed track positions.
2. Related Art
In conventional methods, accuracy monitoring is accomplished by comparing the position report with the position predicted from the trajectory for the given time. If the position difference is greater than some 3-dimensional allowance (termed “conformance bounds”), the trajectory may be regenerated to conform with the position data. However, if the position report is within the conformance bounds, no new trajectory is generated; this is done both for computational efficiency, and to maintain trajectory stability (e.g. for stable alert presentation). The present invention improves on these methods, by improving the accuracy of predicted aircraft conflicts over the first several minutes of lookahead time (tactical alerts) while maintaining both computational efficiency and the stability of predicted conflicts at longer lookahead times (strategic alerts)
An example of a conventional system that uses conformance bounds is the Federal Aviation Administration's User Request Evaluation Tool (URET). URET includes decision support capabilities to assist en route sector controllers to predict conflicts between aircraft (i.e., alerts due to proximity of two aircraft to each other), as well as between aircraft and special use or designated airspace. It also provides trial planning and enhanced flight data management capabilities.
Typically, the information about each aircraft includes its flight plan, current altitude, position, speed, direction, type of aircraft, etc. URET builds a trajectory for each aircraft using this information, atmospheric data, and adapted data (e.g., aircraft performance data, FAA adaptation data). A trajectory is a four dimensional (4-D) representation of the expected path of the aircraft. A trajectory includes a centerline modeled by a time-ordered sequence of cusps that describe nominal 4-D positions (X, Y, Z, t) and conformance bounds (lateral, longitudinal, and vertical distances) that define how far from a nominal position the track position can be before a trajectory is rebuilt. Trajectories are subdivided into segments that represent portions of a trajectory that can be modeled by constant speed, gradient, course, and conformance bounds. Each segment starts and ends at a cusp; the cusps contain the segment modeling parameters.
URET static conformance bounds are a constant magnitude at all lookahead times along a trajectory segment. The conformance bounds depend on the aircraft navigational equipment (e.g., area navigation). Lateral conformance bounds currently extend either 2.5 nautical miles (nm), or 3.5 nautical miles from the trajectory centerline along straight segments, depending on the aircraft navigational equipage. Note also that there is also a vertical tolerance (vertical conformance bounds) and longitudinal tolerance (longitudinal conformance bounds). Lateral and longitudinal conformance bounds are larger than the standard conformance bounds near large turns or for military formations. Vertical conformance bounds are increased near the start or end of altitude transitions. URET trajectories are updated to include observed speed, vertical rates, and course if a track position exceeds any conformance bound (lateral, longitudinal, or vertical) for more than a specified parameter number of consecutive reports.
Alerts are identified by determining if two aircraft trajectory conformance bounds have a loss of ATC separation standards (nominally 5 nm horizontally, and applicable vertical separation distance, e.g., 1000 feet at or below flight level (FL) 290, and 2000 feet vertically above FL290). If the conformance bounds have a simultaneous loss of horizontal and vertical ATC separation distances, the minimum separation distance between the trajectory centerlines is used to identify an alert color (red if the distance is less than or equal to a parameter distance (e.g., 5 nm); otherwise the alert is yellow).
The magnitude of the conformance bounds affects the number of trajectories, the number of correct alerts (alerts where the actual minimum separation distance—if no controller intervention occurred—would be less than or equal to a parameter distance e.g., 8 nm), the number of false alerts (alerts where an actual minimum separation distance would be greater than a parameter distance e.g., 8 nm), and the alert warning time before a predicted conflict start time.
For predicted alerts that start within a few minutes of the “current time,” constant magnitude conformance bounds identify some aircraft pairs with a predicted horizontal minimum separation distance (e.g., 10 nm) that is significantly larger than the Air Traffic Control horizontal separation requirement (e.g., 5 nm). Reducing the size of the conformance bounds will reduce the number of false alerts, but increase the number of missed alerts. Additionally, a reduction in these bounds would reduce trajectory stability. This stability is needed to ensure strategic conflicts do not change unless the aircraft positions are significantly different from the trajectory.
One desired improvement is to reduce the number of displayed alerts without significantly altering the strategic conflict probe notifications. In particular, alerts that have a predicted start time close to the current time (termed “short warning time alerts”) require improvements to better match a continuous track-based update.
Accordingly, there is a need to reduce the number of false alerts in the tactical timeframe, without a corresponding degradation in the number of missed alerts or trajectory stability.